3D Printing Aims to Deliver Organs on Demand

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Dying patients could someday receive a 3D-printed organ made from
their own cells rather than wait on long lists for the short
supply of organ transplants. Such a futuristic dream remains far
from reality, but university labs and private companies have
already taken the first careful steps by using 3D-printing
technology to build tiny chunks of organs.

Regenerative medicine has already implanted lab-grown skin,
tracheas and bladders into patients — body parts grown slowly
through a combination of artificial scaffolds and living human
cells. By comparison, 3D-printing technology offers both greater
speed and computer-guided precision in printing living cells
layer by layer to make replacement skin, body parts and perhaps
eventually organs such as hearts, livers and kidneys.

" Bioprinting
organs for human uses won't happen anytime soon," said Tony
Atala, director of the Wake Forest Institute for Regenerative
Medicine in Winston-Salem, N.C. "But for tissues we've already
implanted in patients — structures we've made by hand — we're now
going back to those tissues and saying 'We know we can do better
with 3D
printing.'" [ 7
Cool Uses of 3D Printing in Medicine ]

From skin to hearts

The difficulty of building organs with 3D printing falls into
about four levels of complexity, Atala said. Flat structures with
mostly one type of cell, such as human skin, represent the
easiest organs to make. Second, tubular structures with two major
cell types, such as blood vessels, pose a greater challenge.

A third level of complexity arises in hollow organs such as the
stomach or bladder, each with more complicated functions and
interactions with other organs. Finally, the fourth level of
complexity includes organs such as the heart, liver and kidneys —
the ultimate goal for bioprinting pioneers.

"With bioprinting, we're approaching it the same way we did with
other organs," Atala told LiveScience. "We're going after flat
structures first like skin, tubular structures like blood vessels
next, and then hollow, nontubular organs like bladders."

Regenerative medicine has already proven it can implant lab-grown
versions of the first three types of organs into patients. Atala
and other researchers hope that 3D printing's efficiency can
scale up the manufacturing of such organs for widespread use, as
well as help make hearts, livers and kidneys suitable for
implanting in patients.

How to print an organ

Atala's group previously built lab-grown organs by creating
artificial scaffolds in the shape of the desired organ and
seeding the scaffold with living cells. They used the technique
to grow artificial bladders first implanted in patients in
1999, but spent the last decade building
3D printers that can print both an artificial scaffold and
living cells at the same time — a process that involves liquid
"glue," which hardens into the consistency of gummy candy as it
dries out.

Other labs think they can bypass the artificial scaffolds by
harnessing living cells' tendencies to self-organize. That avoids
the challenge of choosing scaffold material that can eventually
dissolve without affecting the living cells, but leaves the
initial structure of living cells in a delicate position without
the supporting scaffold.

"If you do what we do with putting cells in the right place, you
don't start with anything structural to hold things up," said
Keith Murphy, chairman and CEO of Organovo, a startup San
Diego-based company. "For us, the challenge is the strength and
integrity of the structure."

Organovo scientists have experimented with building tiny slices
of livers by first creating "building blocks" with the necessary
cells. The company's 3D printers can then situate the building
blocks in layers that allow the living cells to start growing
together.

Stem cells taken from a patient's fat or bone marrow can provide
the 3D-printing material for making an organ that the body won't
reject, Murphy said. His company worked with Stuart Williams,
executive and scientific director of the Cardiovascular
Innovation Institute in Louisville, Ky., on extracting the stem
cells from fat.

The tiniest challenges

The ability to print full-size functioning organs depends on
figuring out how to seed
3D-printed organs with both large and small blood vessels
that can supply nutrient-rich blood to keep living tissue
healthy. So far, no lab has succeeded in 3D-printing organs with
the network of blood vessels necessary to sustain them. [ Photos:
Printing Tiny Organs for 'Body on a Chip' ]

Organovo has begun working toward that goal by experimenting with
3D-printing blood vessels 1 millimeter or larger in width. The
company has also built tissues containing tiny blood vessels
about 50 microns or smaller (1 millimeter is equal to 1,000
microns) — enough to sustain a millimeter-thick chunk of organ.

Even the best 3D
printers remain limited when working on the tiniest scales of
building blood vessels and organs. But Williams, head of the
Cardiovascular Innovation Institute's effort to create a
3D-printed heart, agreed with Organovo that the solution involves
harnessing the self-organization tendencies of living cells.

"We will be printing things on the order of tens of microns, or
more like hundreds of microns, and then cells will undergo their
biological developmental response in order to self-organize
correctly," Williams said. "Printing is only going to take us
partway."

For now, bioprinting pioneers hope to make use of even the
smallest 3D-printed organs. Atala's lab recently received U.S.
Department of Defense funding for a collaborative project aimed
at printing tiny hearts, livers and kidneys to form a connected
" body
on a chip " — ideal for testing possible drugs and the effects
of diseases or chemical warfare agents on the human
body.

Organovo has already started developing a 3D-printed liver model
for testing the safety and efficacy of drugs. The startup company
is also creating cancerous versions of living tissue models for
testing cancer drugs.

The bioprinting revolution could eventually begin to deliver
"tissue on demand" within the next 10 or 15 years, Murphy said.
That may not fulfill the wildest of organ implantation dreams,
but for many patients, it may prove life-changing enough.

"You'll see a heart muscle patch, a blood vessel for bypass or a
nerve graft to bridge a gap in a nerve," Murphy said.